The effects of postfire regeneration patterns on soil microbial metabolic limitation based on eco-enzyme stoichiometry in the boreal forest of China

Abstract

Postfire regeneration is essential for maintaining the stability and functionality of forest ecosystems following wildfires. However, it is unclear whether regeneration patterns affect carbon (C), nitrogen (N), or phosphorus (P) limitations on microbial metabolism in the soil. In this study, we investigated the soil extracellular enzyme activities (EEAs) in different forest types regenerated by five patterns (Dahurian larch monocultures, Dahurian larch and birch mixed plantations, Mongolian pine monocultures, Mongolian pine and birch mixed plantations, and naturally regenerated forests). Based on the principles of ecoenzymatic stoichiometry, we elucidated the spatiotemporal variation in energy (C) and nutrient (N or P) limitations on soil microbial metabolism by collecting a total of 135 composite soil samples across three seasons in the five regeneration patterns. The regeneration pattern had a significant effect on the activities of C-, N- and P-acquiring soil extracellular enzymes (P<0.05). The P-acquiring enzyme activity was 2.71 times greater than the C-acquiring enzyme activity and 3.44 times greater than the N-acquiring enzyme activity across all forest types and seasons. The activities of microbial metabolic C-, N-, and P-acquiring enzymes showed similar seasonal dynamic patterns, with the exception of L-leucine aminopeptidase. In all forest types, the activities of enzymes responsible for acquiring C, N, and P were linearly correlated with one another according to the findings from standard major axis regression analysis (P<0.001). The values of the enzymatic vectors were greater than 45°, indicating that P rather than N was the dominant constraint on soil microbial metabolism. Forests with mixed regeneration patterns had greater P limitations than did the corresponding monoculture forests. Soil temperature was the common soil variable affecting the activities of EEAs across seasons, while the contents of soil organic carbon, dissolved carbon, ammonium nitrogen, and nitrate nitrogen were the significant driving factors of EEAs in a single season. However, forest productivity, including tree density, stand basal area, and forest stand volume had a predominant influence on microbial metabolic P limitation. This study suggests a pronounced role of P in soil microbial metabolism within boreal forests regenerated after wildfires.